CA2192951A1 - Durable coating compositions - Google Patents

Abstract

Coating compositions based on low molecular weight anhydride resin having pendant non-cyclic anhydride moieties, epoxy resin and active catalyst exhibit improved performance characteristics through the inclusion of stabilized acrylic resin.

Description

~ WO 96/01880 PCTNS9S/07124 Im~
D'IJRABLE COATING CO-MPOSITIONS

BA~('lROl~ND OF THE INVENTION
The present invention relates to a curable coating particularly useful as a top coat in multi-layered coating systems.
Base coat-clear coat systems have found wide r~ e in the past decade as a.l~ullwlivO finishes. Cnntin~ing effort has been directed to such coating systems to improve the overall r~al~.,~" the clarity of the top coat, and 10 the resistance to .1. ~. . ;. r I ;~ ~ ~ Further effort has been directed to the d~lu~ of coating r~ having low volatile organic content (VOC).
Previous efforts at improving the etrh resistance and durability of coatings had suggested the use of anhydride resins having pendant non-cyclic anhydride moieties in çon~ ti~-n with resins that react with the pol~allllJ.llidc resins to cure under curing rnnrlitinnc However, a continuing need exists for coating ~ which can be sprayed at low VOC and which exhibit l .".l;"g p.. r.. ~. ~ characteristics after ~pplir~tirn and particularly resistance to CllVllUll~ .l etching.

S~MM/~RY OF THF INVFNTION
The present invention provides a sprayable coating ~ r~
which can be easily applied at high solids and exhibits u~ g a~y~,al dll~
and durability after ,.~ l i.... and ease of ..,~i.,l..,,".. ~
Specifically, the instant invention provides â curable coating 25 cullllJoaiLion rr., ~ organic solvent and binder, the binder r u~
(a) anhydride resin having a molecular weight of less than about 3000 that contains (1) a central moiety, and (2) on average, more than one pendant, non-cyclic anhydride moiety bonded to each central moiety;
(b) oligomer having epoxy filn~tion~lify of at least 2 and having a 30 molecular weight of less than about 1500;
(c) about from 3 to 40%, by weight of the binder, of stabilized ~ acrylic resin having (i) a core of acrylic polymer which is non-soluble in organic solvent and, grafted thereto, (ii) a plurality of ~ -hct~nfi~lly linear stabilizer .. "l.,~
having an acrylic backbone and at least about 3%
ethylenically ul~Lul~lLcd monomers containing epoxy r ' ~ ~ t each of which is soluble in organic solvent and has onc end grafted to the corc, the stabilized acrylic resin being ~ lly free from non-p~ linear polymer; and S(d) a functional amount of at least one active catalyst, wherein the ratio of eiui~ of epoxy to anhydride is about from 0.5to 1.8.

DPTAII Fl ) DESCRIPrlON OF T~F. INVFl~TION
Anhydride resins which can be used in the present invention include 10 those having a molecular weight of less than about 3000 having a central moiety and more than one pendant, non-cyclic anhydride moiety bonded to each central moiety. The anhydride is :l~ymm.otnr~l and preferably contains a moiety .,s~ ,d by tbe following formula.

CM~C--O--C--R1 )"

wherein (CM) is a central moiety, (Rl) is an organic moiety, and n is a number of pendant arhydride groups that averages greater than one.
The central moiety can be a simple organic moiety, such as an 20 aliphatic, cycl~ lirll~tir or aromatic moiety, with a plurality of anhydride groups bonded to it. Al~ .a~ ly, it can contain a plurality of repeating units which are bonded to one or more pendant anhydride groups. _xamples of suitable non-polymeric central moieties are those derived from ",..1~ir," ~ l alcohols such as pc~ y~l.li~ol, LlhllC~ ollJlu,udllc and neopentyl glycol. The .. ,ll ir.. , ion~l 25 alcohols are reacted with cyclic, mr)n~m~ anhydride such as methyl hexahydl u,ull~lldliC anhydride to give a m~ i r.. 1 ;.~ acid containing moiety.
Tbe resulting product is then reacted with ketene to form tbe linear pendant anbydride.
The central moiety is linked to more than one non-cyclic anhydride moiety, on average. It is preferably linked to at least about 2 non-cyclic anhydride groups on average and more preferably to at least about 3 non-cyclic anhydride groups on average. The anhydride equivalent weight (formula weight per anhydride group) is preferably at least about 200 and preferably no more than about 1000.
Each anhydride moiety is typically ~ d by an organic group, which is preferably aliphatic and more preferably alkyl. It preferably contains no ,,, . , , . , . , , .. , ... _ .. , . , . _ . . .. . . . .. . _ _ _ _ _ _ ~wos6/olsso - 2 1 9295 1 ~.",~ ,.24 more than about 6 carbon atoms, more preferably no more than about 4 carbon atoms, and most preferably methyl.
T~ ol;6v...~.;c l~di:~ C~n optionally c(..A~.h. n l;~A~ .~..;
organic moiety (A) that is linked to a plurality of anhydride groups by a plurality/
5 of pendant linking groups (L~), as illustrated in the following formula: /

O O
AtLG--C--O--C--R1 )n wherein Rl is an organic group of 1-10 carbon atoms. The li~group (LG) can 10 contam, for example, ester linkages, alkylene groups, ether lir~fages, urethane linkages and 1~ ....l .; ..~ 1 ;....~ of those. The polyvalent organ~/group can contain, for example, a polyvalent alkyl or aromatic group. The ~mhinsltir~n of the polyvalent organic moiety (A) and the linking groups,Ç~G) forms the central moiety (CM) as previously described.
The central moiety can optionally ~ontain other functional groups in addition to the pendant non-cyclic anhydrid~e'groups. For exarnple, the central moiety may contain pendant acid groups, so~hat the anhydride is r~ ,s~.ltcd by the formula:

f M~--O--C--R1 )n ~2H)m wherein m is the number~pendant acid groups and all other characters have the meaning previously gi~n. The molar ratio of pendant non-cyclic anhydride groups to pendant a,~d groups in the oligomeric anhydride is preferably at least25 about 25:75~ ul,5~ul~ 1.r at least about 50:50, and more highly preferably at least about 75~5. Most preferably, the anhydride contains cnhctanti~lly no pendant aciy~luul,s. The central moiety can also contain minor quantities of cyclic anh~dride moieties.
The molecular weight of the anhydride resin should be less than 30 abou,~3000. At molecular weight. of the oligomeric anhydride greater than 3000, it,~difficult to attain a sprayable ~;Ulll~JU:>iLiUII with a volatile organic content of ~léss than about 3.5 pounds of organic solvent per gallon of curable culll~,u~iLiul~, / which is often preferred for high solids coatings The molecular weight of the ~ L;dc .~ ... is prefer:lbly le ~ n ~bout 2000, ?nrl e~.o~ lly ~h~ ~ from 100 2 1 q2q5 1 ~

The oligomeric anbydride can optionally contain a polyvalent organic moiety (A) that is lir~ed to a plurality of anhydride groups by a plurality of pendant linl~ing groups (LG), as illustrated in the following formula:

S t wherein Rl is an organic group of 1-10 carbon atoms. The lir,king group (LG) cancontain, for example, ester linkages, alkylene groups, ether lirkages, urethane li~kages and cul,lbiu~Lio~ of those. The polyvalent organic group can contam, for 10 example, a polyvalent alkyl or aromatic group. The c.~ l,;"~l;.", of the polyvalent organic moiety (A) and the linking groups (LG) forms the central moiety (CM) as previously described.
The central moiety can optionaUy contain other functiorlal groups in addition to the pendant non-cyclic anhydride g}oups. For example, the central 15 moiety may contain pendant acid groups, so that the anbyclride is ~c~ cd by tbe formula:

O O '' CM~C--O--C--R1 )n (CO2H)m wherein m is the number of penclant acid groups and aU other characters have tbemeaning previously given. The molar ratio of pendant non-cyclic anbydride groupsto pendant acid groups in the oligomeric anhydride is preferably at least about 25:75, more preferably at least about 50:50, and more highly preferably at least about 75:25. Most preferably, the anhydride contains sllhcr~nti~ y no pendamt acid groups. The central moiety can also contain minor quantities of cyclic anhydridemoieties.
The molecular weight of the anhydride resin should be less than about 3000. At molecular weights of the oligomeric anhydride greater than 3000, it is difficult to attain a spTayable . ~ with a volatile organic content of less thanabout 3.5 pounds of organic solvent per gallon (0.42 kg/l) of curable ~uul~O~;LiOlls~
which is often preferred for bigh solids coatmgs The molecular weight of the anhydride resin is preferably less than about 2000, and especiaUy about from 400 to AMENED SHEET

_ _ _ . . _ , . ... ......... .. ... .... ..

~ WO 96/01880 2 1 9 2 9 5 1 PCIIUS9~/07124 to 1,000. The anhydride resin preferably has 3 to 4 pendant, non-cyclic anhydride moieties bonded to each central moiety.
The oligomer ~ contains at least two epoxy groups and should have a molecular weight of less than about 1500. Typical epoxy S ~ include sorbitol pO'i~b'i~,~,hlyl ether, marmitol polyglycidyl ether,p.,-l~d~.lyil~ ul pol~ iJyl ether, glycerol pol~ly.,;dyl ether, low molecular weight epoxy resins such as epoxy resins of epi~ ' ' uh,~L iu and bisphenol-A., di-and pol~ ;dyl esters of POI~1JUAYI;C acids, pol~ ;dyl ethers of i~u,~ c, such as "Denecol" EX301 from Nagase. Sorbitol pol~ hlyl ether, 10 such as DOE-358~9 from Dixie Chemical, and di- and pûl~ ,;dyl esters of acids, such as Araldite CY-184~ from Ciba-Geigy, ûr XU-71950 from Dow Chemical are preferred since they form high quality finishes. Cyrln:llirhqtir epoxies canalso be used, such as ERL,4221 from Union Carbide.
The binder further comprises about from 3 to 40%, and preferably 15 about from 10 to 25%, by weight of the binder, of a stabilized acrylic resin having a core of acrylic polymer which is non-soluble im organic solvent and, grafted thereto, a plurality of sllbct~lnti~lly linear stabilizer co~ ull.,llb having an acrylic backbone and at least about 3% ethylenically " ~ d .. ,.. ,, .. ~ containing epoxy filnrtinn~lity, each of the linear stabilizer co--l~u--~.lL~ being soluble im 20 organic solvent and having one end grafted to the core, the stabilizer acrylic resin being snhct~ntiqlly firee of non-pul~ ~able linear polymer. Less than about 3%
does not result in the desired illl,UlU._-Il~,lll in p. . r(., ."_... P rhqrq~tPrjctirc, and little additional benefit is realized at ~;ull~ l aliOI~ greater than about 40%.Typical alkyl acrylates and Ill~.~Ld~ ld~Cs that can be used to form 25 the stabilized acrylic resin are as foLows: methyl methacrylate, ethyl Ill~La~l~la~
propyl Ill~,LLà~lyld~e, butyl methacrylate, pentyl I~ laclylale7 hexyl ...~,LLa~l~lale, octyl Ill~,~la~lyldlc~ decyl methacrylate, lauryl Ill.,lllà~l~lale, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, nonyl acrylate, decylacrylate, lauryl acrylate, hydroxy ethyl acrylate, hydroxy ethyl ~ iLà~l~la~c and 30 the like. Other .;ol--~uul~ b that can be used to form the stabilized acrylic resin are acrylamide, I~ La~lylalllide and acrylo alkoxy silanes such as gamma iLà~ lylyl propyl ~ lU.~,~ silane.
The core of the stabilized acrylic resin can be crosslinked or not crosslinked, according to the desired ~.. . r. " " ,~ characteristics. C~u~lLIhi-lg 35 can be acromrlichPd by a wide variety of -1ifilnrtinnsll " u ,.~ , such as aLyl methacrylate or ethylene glycol diacrylate omlilll~lla~lylàlc or butylene glycoldiacrylate or dimcllla~lyla~e. Crosslinking of the core material can also be ~ . .
. . .

A~ Cnl ~ Sd by reaction of a hydroxy monomer with di- or tri- isocyanate, alone or in ~.."l.,l,~ " with ulu~li~i~ by the ~lifiln~tinnAI monomers noted above.
The particle size of the stabilized acrylic resin can vary widely, but, in general, will range from 100 I~AIIIIIII~ ~1'~ to I micron. Preferably, the particle size S of the stabilized acrylic resrn is about from 100 to 400 IIAIII~III~ '. . ~
The stabilizer . ~I.l,n~ attached to the core are soluble in the polylu.lL6ilLYj solvent medium. These ~ can be linear or branched, and are chernically attached to the surface of the core. In general, the stabilizer CUUI~UII..IL~
have a molecular weight of about from 1,000 to 100,000 and preferably about from 2,000 to 20,000. Typical monomers used for the stabilrzing ~ n~ are acrylates, lu.Lll~ly- , styrene, or glycidyl Lu.Ld~lyl_'~, or glycidyl acrylate.
In a preferred process of preparing the linear stabilizer component used in tbe present invention, cobalt chain transfer agent is used. The preferred catalytic chain transfer agent is a compound which contains Co+2. Exemplary cobalt chelates are those described in U.S. Patent 4,680,352 to Janowicz et al. and U.S.
Patent 4,722,984 to Janowicz. Most preferred chelates are p~LduyAIlncQb diaquabis(buluu.linuulu.lLLu.~llyl-glyoximato) cobaltate (II) and diaquabis(buluLllinuuluL~lle.lylglyu,~iuldLu) cobaltate (II). Alternately, Co+3 chain transfer agents can be used, as described in PCT Patent Appiication W087/03605. _: =
Such chain transfer agents are ordinarily used at ~ ,.u .. 1 ;.. ,~c of 5-150 ppm based on the mnnnmf~r~
Typically, a mixture of monomers and organic liquid is heated, preferably to reflux t~ ,.dLulc for ease of control, and to the mixture is added the catalytic chain transfer agent of choice, additional monomers and solvent, and the usual amount of a CUU~ ULIdI POIYLU~ Un initiator such as an azo- or peroxide initiator. The reaction is run, with additions of monomers and initiator as needed, until the desired stabilized acrylic resins or IIL~.,1. 1111(11 Inl 11. ~ ~ are obtained having the desired molecular weight. Solvents which can be used include aromatic and aliphatic hydlu~ubu~ esters, ketones and mixtures thereof.
The stabilized acrylic resin can be efficiently prepared in a two step process, the second of which can be run iLULU~,IidLely after the first but which is ordinarily run after a pause for analysis and to permit more effcient use of the reactor.
The stabilized acrylic resm is prepared by (a) polymerizing one or more ethylenically Illl~ul~lr~i acrylic mnnnm-~r~, at least one of the monomers containing an epoxy functional group, using a catalytic chain transfer agent containing Co+2 to form a stabilrzer component having an AMENDEO SHEET

2 1 92q5 1 .

ethylenically, ' terminal group and at least one epoxy functional group, and then (b) preparing the core component by po4,~ ,,~0 one or more acrylic monomers while they al(em contact with stabilizer c~ , steps (a) and (b) 5 being conducted in an organic liquid which is a solvent for the stabilizer ~ulll~ollc but a non-solvent for the core component.
In step one, a mixture of stabilizer monomers and organic liquid,is heated, preferably to reflux t~ ldLuL~ for ease of control, and to it is added the catalytic chain transfer agent of choice, any additional monomers and solvent, and AMENOED SHEET

~ WO96/01880 2 1 9 2 9 5 1 I~,J/~

the usual amount of a cu..v ~nt;u~l pol~ initiator such as azo- or peroxide initiators. The reaction is run, with additions of mnnnmlorc and initiator as needed, until the desired stabilizer c ~ 1 is obtained (ordinarily having a Mw of about 2000-20,000, and preferably about 3000-8000).
In step two, an organic liquid which is a solvent for the stabilizer l but a non-solvent for the core ~ n~ is added to the product of step one. "Solvent" and "non-solvent" are used in the, . _Illiul~l sense, as will be nn~lPrctood by those skilled in the polymer art. Illustrative of organic liquids which can be used are aromatic- and aliphatic l., LU~IJUI~ such as heptane and VM&P naphtha Mixtures of liquids can also be used. The stabilizer/liquid ratio is of secondary 1~ but is usually in the range 1/2 to 1/4 (weight).
The resulting mixture is again heated, preferably to reflux , dlUI c for better control, and to it are added the core l ", . ,. " ~ and a conventional initiator such as one of those previously, . .1;, " ,. ~1 in the usual amount. rOI~ ;l--- is continued, with additions of liquid and initiator as needed, until it is complete, as ~f ~ d by periodic sampling and analysis.
The present c~ contain a functional amount of at least one active catalyst. rd~ y beneficial in the present invention are tertiary amine catalysts such as triethylene diamine, Bis(2-dimethyl dllPillu~ l)ether and 20 N,N,N1, N1 t~,LId~ lLyl~ hyh ~ ,;"~
The active catalysts can be used alone or in ~ -, "l .;, - l ;, ,- - with one or more additional catalysts, such as onium ~,...l.,,".,ll~ including U,udt~ uy rl~ h~ and~ludt~l~y Examplesofl~hr.~l.l.~...:, catalysts which can be used in catalysts blends in ac~,l J~l.C with the present invention are 25 benzyl triphenyl ph~ 8~ chloride; ethyl triphenyl pl.. ~ h. : ~". bromide;
tetra butyl ~ l.h, .";.".. chloride; tetra butyl pl.. ~ bromide; benzyl triphenyl i ' l ' iodide; benzyl triphenyl r~ .,. ".. bromide; ethyl ~riphenyl rl.. ~l.h.. :.. iodide and the like.
The c ~ of the present ~ l-u~ are adjusted in 30 quantity to provide a ratio of e~luivalullcc of epoxy to anhydride of about from 0.5 to 1.8, to provide good p. . r, ll ~ characteristics in the cured coating.
The coating CUIII~JO~iiiUlla of the present invention are r ~ Jt- d into high solids coating systems dissolved in at least one solvent. The solvent is usually organic. Preferred solvents include aromatic LyJlu~dllJul~ such as 35 petroleum naphtha or xylenes; ketones such as methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone or acetone; esters such as butyl acetate orhexyl acetate; and glycol ether esters such as propylene glycol, l- - " ". l hyl ether acetate.

-The coating ~nmpoCitinnc of the present invention can also contain eu~ .lLiulldl additives such as pigments, stabilizers, rheology control agents, flow agents, toughening agents and fillers. Such additional additives will, of course, depend on the intended use of the coating o~ ". ,l,n~ ., Fillers, pigments, and other additives that would adversely effect the clarity of the cured coating will not be included if the ~"~ n~ "~ is intended as a clear coating.
The (.~ J~ of the present rnvention generally have a volat~le organic content of less than about 3.8 pounds of organic solvent per gallon (0.46 kg/l) of curable c~ " that is, at least about 50 wt % solidc. The coating 0 CùlulJo~i~iu~S are typically applied to a substrate by cu~ iul~l techniques such as spraying, el.~Llu~Ld~i-, spraying, roller coating, dipping or brushing. The present fnrmnl~finnc are pdu~i~ukuly useful as a clear coating for outdoor articles, such as duLu~obilc and other vehicle body parts. The substrate is generally prepared with a primer and or a color coat or other surface ~IC~dldLiull prior to coating with the present c l " ~ .lln~ The present coating ~,UIIl~/UsiLiUllb can be applied using~u u~ ~llLiulldl techniques such as wet-on-wet du~lica~iullb over solvent borne basecoats, or over dried water borne basecoats. The ability to apply the presentu~ n~ by spraying techniques with the unusually low VOC content is surprising. : s 2û After application to a substrate, the present . v~ n~ are cured by heating to a telll~ldlulc of about from 125 to 140~C for a period of about from 15 to 90 minutes.
The pf r." ",~". e Ci1'~ 6~ C of the fin~l cured coating LUlll~U~iLiUU
are excellent, providing a ~~ULUbiUdLiUU of excellent gloss and durabiliy to abrasion, sunlight and acidic rain. The addition of non-aqueous dispersion or stabilized acrylic resin component in the present ~ulll~o~iLiuu improves the rheology control of the r~" ",."~i.,.. reducing or eliminating the need for separate rheology control agents of the type previously used. Moreover, these . .. ,l,.." ,1~ reduce the stress in the fmished coating, thereby improving the crack resistance of the coating on outdoor 30 exposure. At the same time, the uuLu~ubiLiul~ provide ease of handling, resulting from all the CoLul)u~ lLb being present in a single fnrm~ rinn, good shelf life and low volatile organic content.
The present invention is further illustrated by the following specific examples, in which parts and p ~ ,., are by weight unless otherwise indicated.
35 Molecular weight, as used herein, unless otherwise indicated, refers to weight average molecular weight, as ~iPrf nninf ~i by gas phase ~lu~ l y .

A~iiENDED SHECT

~ WO 96/01880 ~ v /124 FxAMPl~F~ 1 A curable coating ~ c, I ~( ~, was prepared from an anhydride resin, rllienmPri~ epoxy resin, stabilized acrylic resin and active catalyst. These c~ were prepared as follows.
(a) Arhytlride~.ocin An anhydride resin was prepared from a tetra-functional half-acid ester. The following ~ were charged to a reaction vessel equipped with a heating mantle, reflux condenser,1l~ ,...,, t- , nitrogen inlet, and stirrer:

portion 1 Parts by W~i~ht PellLelyLllliLùl 478.0 Methyl hexah.,~Lul.LLLalic anhydride2250.0 Tr.cLL.~' ~ 0 5 Portion 2 P~rts by W~ ht Xylol (135-145C) 2250.0 Total 4978.5 Portion 1 was charged into the reaction vessel, heated to 180~ C
under a nitrogen blanket and held for 30 minutes. After the hold period, the reaction mixture was cooled and Portion 2 added.
The solution prepared above was used to make a linear pendant anhydride. The solution was charged into a 5L flask equipped with a stirrer and a gas inlet tube. the gas inlet tube was attached to a ketene generator similar to the one described by Williams et al. in the Journal of Organic Chemistry 5,122, 1940.
Ketene is bubbled through the solution until aU of the acid groups have been converted to anhydride groups. Reaction progress was monitored via ~
Solvent was then removed under vacuum to give a linear pendant anhydride with the following ~ ~ - t~

~o weight solids: 78.0 Anhydride eq. wt: 329 + /~ (on solution basis) Acid eq. wt: 6176 +/- 1323 (on solution basis) ; . . ~

~ WO 96/01880 PCTNS95/07124 (b) St~hili7~ A Acrylic Resin FIC~ of l~oh:~ltM.. ~
To a 2-liter flask fitted with an agitator, c~ nA -nc-r, heating mantle, nitrogen inlet, Ih~ V 1~lr and an addition port was added 81.29 gms. butyl 5 Ill~iLa~ lyl~t~ 243.88 gms. 2-ethyl hexyl Lh~ ILà~ lylaLc, 81.29 gms. glycidylu~ iL~.~ lylaLe~ 210 gms. toluene and 50.1 grns. butyl acetate. The rnixture wasagitated and heated to reflux (135-140~C) under nitrogen. To this was then added, in one portion, a pre-rnix of a solution of 0.35 gms. Vazo~9 88, 13.8 gms.
toluene and 17.2 gms. of a 0.17~o solution of bis(Boron Difluoro Diphenyl 10 Glyoximato Cobaltate (II)) in methyl ethyl ketone. This was followed by the addition of a pre-mix of a solution of 71.34 gms. butyl ul~Lll~l~lylalc, 214.02 gms. 2-ethyl hexyl lll~ La~ Iylat~" 7134 grns. glycidyl Ll~. LLaclyldLe~ 1.35 gms. Vazo!9 88 and 86.8 gms. toluene over 240 mins. while .,,~, I~; ....~ reflux (116-122~C).
Following a 30 rnin. hold period, a pre-mixed solution of 032 gms. Vazo~) 88 and23.0 gms. toluene was added over 60 mins. while, ;"ls ~ reflux. The batch was then held at reflux for an additional 60 rnins. at which time a rnixture of 0.23 gms. t-butyl p~.v~Lo~lLe and 31.5 gms. of butyl acetate was added in one portionand the reaction mixture then cooled. The LUaCl"" " ~' '"" ' ~ thus prepared has a number average molecular weight of 3400 and a weight average molecular weight of 5500 as APt- r~in~d by GPC. Weight solids are 63.6% and Gardner viscosity F.
The percent terminal vinyl ~ - is >95 as ~ d by Il.... ...",r.~ hu.,LIic analysis.

P~ L;.J.... .........of Stabilized Acrvlic Resin To a 2-liter flask fitted with an agitator, conA~nc~ r heating mantle, nitrogen inlet, 11,~ v~l.le and an addition port was added 222.32 gms. of cobalt ma~l v .. .~ ." .- prepared above and 394.4 gms. heptane and the L~ iulc raised to reflux (95~C) under nitrogen at which time 0.55 gms. t-butyl peroctoate was added in one portion. This was followed by the addition of a 30 premixed solution of 96.63 gms. methyl ~ ;L~I~1YIaLCI 59.16 gms. styrene, 47.33 gms. hydroxy ethyl acrylate, 70.99 gms. methyl acrylate, 39.44 gms. acrylonitrile, 1.97 gms. allyl ul~;LG. lyL.Le, 78.88 gms. glycidyl methacrylate, 110.43 gms.
,lVulVllvLUC. of Example 1, 5.92 gms. t-butyl peroctoate and 63.7 gms toluene over 210 mins. holding reflux at 95~C. This was followed by a hold period of 45 35 mms. at reflux at which time a premixed solution of 3.94 gms. t-butyl peroctoate and 28 gms. toluene was added over 30 mins. while . . ~ .g reflux. The reaction mixture was then held at reflux for 60 mins. followed by distillation of 78.88 gms. solvent to raise weight solids to 54%. Particle size as measured by I ~

quasi elastic light scattering was 206 ~ Gardner Holdt viscosity was A2.
I)u~l Crn~linkP~I St~hili7~fl Ar~ylic ~cin ~ To a 2-liter flask fitted with an agitator, condenser, heating mantle, 5 nitrogen inlet, ~ 0~ lr and an addition port was added 500 gms. of stabilized acrylic resin prepared above and the Lelllpc,dLul~ raised to 90~C at which time 12.5 gms. of D,ES3390~9 isocyanate and 5 gms. methyl ethyl ketone was added over,10 mins. The reaction mixture was held at 90~C for 4 hrs. until all the isocyanate had been consumed as measured by IR. 45 gms. of solvent were then distilled to raise10 weight solids to 60% and the reaction mixture cooled. The crosslinked stabilized acrylic resin had a Gardner Holdt viscosity of J.

(C) C~tiT~ C~ no~itil~n A clear coating preparation was prepared by combining two 15 fnrTmll~tionc, designated as the anhydride r~" "",~ .", and the epoxy rulluuldLiull below. In those fonmll~tion~, the linear pendent anhydride and the stabili_ed acrylic resin were prepared as described above.

Anlly-~ri~ Fonnnl~fion Linear Pendant Anhydride 63.4 Tinuvin 384 1.9 Tinuvin 292 1.5 20 % BYK-301 (flow add from BYK chemie) in PM Acetate 1.4 24% tetra butyl phos cl in PM Acetate 1.7 F~rox,v r~ ""l~

XU-71950 (Diglycidyl ester from DOW) 31.6 Stabilized Acrylic Resin 27.8 Butyl Acetate 24 This clear was sprayed over prebaked ~ t~bullle basecoat (10 min at 82~C
(180~E:)) and cured for 30 min. at 141~C (285~E~). The resultmg film had good All~). ~.1.11111-, hardness, and chemical resistance.

A~ riy~i) c l~ ~

Claims (8)

1. WE CLAIM:
   A curable coating composition comprising organic solvent and binder, the binder comprising (a) anhydride resin having a molecular weight of less than about 3000 that contains (1) a central moiety, and (2) on average, more than one pendant, non-cyclic anhydride moiety bonded to each central moiety;
   (b) oligomer having epoxy functionality of at least 2 and having a molecular weight of less than about 1500;
   (c) about from 3 to 40%, by weight of the binder, of stabilized acrylic resin having (i) a core of acrylic polymer which is non-soluble in organic solvent and, grafted thereto, (ii) a plurality of substantially linear stabilizer components having an acrylic backbone and at least about 3%
   ethylenically unsaturated monomers containing epoxy functionally, each of which is soluble in organic solvent and has one end grafted to the core, the stabilized acrylic resin being substantially free from non-polymerizable linear polymer; and (d) a functional amount of at least one active catalyst, wherein the ratio of equivalents of epoxy to anhydride is about from 0.5 to 1.8.
2. 2. A composition of Claim 1 wherein the stabilized acrylic resin is prepared by (a) polymerizing one or more ethylenically unsaturated acrylic monomers, at least one of the monomers containing an epoxy functional group, using a catalytic chain transfer agent containing Co+2 to form a stabilizer component having an ethylenically unsaturated terminal group and at least one epoxy functional group, and then (b) preparing the core component by polymerizing one or more acrylic monomers while they are in contact with stabilizer components, steps (a) and (b) being conducted in an organic liquid which is a solvent for the stabilizer components but a non-solvent for the core component.
3. 3 A composition of Claim 2 wherein the chain transfer agent is a colbalt +2 or cobalt +3 chelate.
4. 4. A composition of Claim 3 wherein the chelate is selected from a pentacyanocobaltate (II), diaquabis(borondifluorodimethyl-glyoximato)cobaltate (II) and diaquabis(borondifluorodiphenyl-glyoximato)cobaltate (II).
5. 5. A composition of Claim 1 wherein the active catalyst is at least one compound selected from the group consisting of onium compounds and tertiary amines.
6. 6. A composition of Claim 1 wherein the binder comprises about from 10 to 25% stabilized acrylic resin.
7. 7. A curable coating composition of Claim 1 applied to a substrate.
8. 8. A coated substrate of Claim 7 wherein the applied curable composition is substantially free from pigment.